Solvent extraction of petroleum oils



Filed April 21, 193'! 08 MMH MMMM VISCOSITY GRAVITY CONSTANT INVENTORS JOHN M. RUSS, JR. HARVEY R. FIFE BY ATTORNEY Patented Aug. 6, 1940 UNITED STATES 2,210,383 SOLVENT EXTRACgEN OF PETROLEUM John M. Russ, Jr., and Harvey R. Fife, Pittsburgh, Pa., assignors to Carbide and Carbon Chemicals Corporation, a corporation of New York Application April 21, 1937, Serial No. 138,068

. Claims.

This invention relates to the refiningv of petroleum lubricating oils by solvent extraction. Broadly, it comprises an improved method for removing the naphthenic from the paraflinic con-.

5 stituents in oil stocks by selective solvent action, and the process of this invention is particularly suitable for the refining of oils high in naphthenic substances.

As lubricants, the parafllnic portions of pew troleum oils are much superior to the naphthenic,

since the paraflinic oils have the property of witho- 0.24+0.022 g (V35.5)] 0.755

where a is the constant, G the specific gravity at 60 F., and V is the viscosity in Saybolt seconds at 210 F. Highly parailinic oils have low viscosity so gravity constants, while highly naphthenic oils have high viscosity gravity constants. The greatest extraction efficiency is reached when a maximum yield of oil having the lowest viscosity gravity constant is obtained, and an ideal selective solvent for such a process is one in which the paraflinic hydrocarbons are insoluble and the naphthenic hydrocarbons completely soluble. Under practical conditions of refining, another factor enters into the problem and that is the 49 relative amounts of paraflinic and naphthenic constituents present in the oil. The oil constituents are, of course, mutually soluble, and when naphthenic material is dissolved in the solvent the solubility characteristic of the mixture is inter- 45 mediate to the solvent characteristics of the individual materials. Thus a mixture of solvent and naphthenic material dissolves a certain amount of the parafiinic oil, and also an oil containing a mixture of naphthenic and paraflinic material 60 will dissolve a certain amount of the solvent. The amount of paraflinic material dissolved in the solvent, or extract phase, increases with increase in the concentration of naphthenic material in that phase. Certain oils may contain so much 66 naphthenic material that the oil and solvent are miscible at ordinary temperatures and, in order to effect phase separation, cooling or alteration of the properties of the solvent by the addition of one or more components may be necessary. In

.0 altering the properties of a solvent by the addition of other components, it is desirable to add materials which increase the selectivity of the solvent to the maximum extent.

Of the various liquids that have been employed as solvents in such refining processes, it has been found that p,,3-dichlorethyl ether is one of the most selective and, therefore, most efllcient. This ether is used with much success in the refining of highly paraflinic oils, suchas those from Pennsylvania crudes. Mid-Continent oils may also be refined advantageously with this solvent. Due to-the high content of naphthenic materials in Gulf coastal, California, and similar type oils, the miscibility temperature of p,p'-dichlorethyl ether and these oils is so low that refrigeration is required to effect satisfactory phase separation. Refrigeration is cumbersome and'costly and is to be avoided when possible.

It is an object of this invention to provide selective solvents of vsuch characteristics that efficient phase separation of oils containing high proportions of naphthenic constituents may be effected at ordinary temperatures.

A further object is to provide selective solvents of such character that the separation of the naphthenic and paraflinic portions of higher grade crude .oils may be obtained with greater efficiency than heretofore.

Other objects of the invention are apparent from the following description.

The solvents of this invention may be made by mixing p,p-dichlorethyl ether with certain other liquids which may or may not be in themselves selective solvents suitable in some degree for the refining of lubricating oils. In particular, it has been found that mixtures of p,fl'-dichlorethyl ether and methanol or p-methoxy ethanol have selective solvent properties greater than dichlorethyl ether alone. This is indicated in the following table of data obtained from tests with equal volumes of oil and mixed solvents. In this table the temperaturesrepresent the highest temperatures that phase separation would take place with dichlorethyl ether, with mixtures of equal volumes of the ether with methanol, and with methoxy ethanol.

To illustrate more comprehensively the improvement in extraction efficiency of these two mixed solvents over dichlorethyl ether alone, the

accompanying drawing shows the results of single batch extractions at difierent temperatures oi. a Mid-Continent untreated distillate which had the following properties:

Specific gravity 60/60' F 0.9053 Viscosity 210 F., Saybolt secnds 50.5

Viscosity 100 F., Saybolt seconds 331.0 I Viscosity gravity constant 0.8469

The curves indicate the variation in quality of product (viscosity gravity constant) and percent yield, with change in the solvent-to-oil ratio. The numbers I, 2 and 3, on the curves indicate the solvent-to-oil ratios of 1, 2 and 3, respectively, at the corresponding points on the graph. Curves A, D and G indicate the extraction eiiiciencies obtained with dichlorethyl-ether alone at temperatures of 45, 35 and 25 C., respectively; curves B, E and H indicate the extraction efliciencies obtained with a mixture of 80% of the ether and 20% by volume of methoxy ethanol likewise at 45, 35 and 25 C., respectively; and curves C, F and J represent the extraction efliciencies obtained with a mixture of 80% of the ether and 20% by volume of methanol at the temperatures of 45, 35 and 25 C., respectively.

The choice between methanol and methoxy ethanol in preparing mixtures with dichlorethyl ether, and the ratios of the constituents in the solvent mixture depend upon the oil to be extraced and conditions of extraction.

Methanol has a low boiling point and does not form constant boiling mixtures with water, and therefore may be more suitable where the oil extract comes in contact with water during the refining process. Since the specific gravity of B- methoxy ethanol is relatively high (0.9660 at 20/20 C.) higher ratios of this solvent to the ether may be used, and such mixtures generally exhibit less tendency to emulsiiy with the oil than do mixtures of dichlorethyl ether and methanol.

It has been found that usually from 20% to 50% by volume of methanol or methoxy ethanol in the mixture with dichlorethyl ether will give satisfactory results. The ratios of solvent to oil which may be used satisfactorily in this process depend upon the composition of the crude oil to be treated and the temperature of operation.

In general, it is desirable to obtain a balance between solvent composition, solvent-to-oil ratio, and temperature which will give a maximum yield of oil having the required quality.

In practice, the countercurrent principle of extraction is used, either in the form of continuous countercurrent towers or as continuous countercurrent stages. In cases where miscibility temperatures permit, the most eflicient utilization of a diluent for dichlorethyl ether is realized when the diluent is added at some intermediate point in the system. This procedure alloys the production of a parafllnic material of minimum specific gravity and a naphthenic extract of maximum specific gravity. The parafllnic, or high grade portion of the oil, obtained as one of the two liquid phases from the extraction process, is usually distilled to remove the small quantity of contained solvent, and the solvent phase from the extraction process is also distilled to separate the solvent from the naphthenic oil, for reuse.

The separation of the oil into naphthenic and parafiinic components may be done either before or after other refining treatment. That is, the oil may be first dewaxed and decolorized and then separated or it may be subjected to the usual refining methods after selective solvent extraction of the naphthenic and parafiinic components. However, the solvent mixtures of this invention are suitable for the extraction of petroleum oils by any of the engineering practices known in the art, and many modifications of the process may be made within the scope of the invention as defined by the appended claims.

We claim:

1. In the process of refining petroleum oils by solvent extraction, the step which comprises treating the oils with a mixture 01' p,fl'-dichlorethyl ether and p-methoxy ethanol.

2. In the process of refining petroleum oils by solvent extraction, the step which comprises mixing an oil containing both naphthenic and paraffinic constituents with a selective solvent composed of ,6,p-dichlorethyl ether and p-methoxy ethanol, agitating the mixture to form a solution wherein an oil of high viscosity gravity constant is dissolved in the solvent, then separating said solution from an oil having a low viscosity gravity constant, and separately distilling said selective solvent from the resultant products.

3. The method of preparing lubricating oils of low viscosity gravity constant which comprises intimately mixing a lubricating 011 stock containing both naphthenic and parafiinic hydrocarbons with a selective solvent composed of 50% to 80% fl,p'-dichlorethyl ether and 50% to 20% ,s-methoxy ethanol by volume; effecting separation between the selective solvent phase containing dissolved naphthenic hydrocarbon, and paraffinic oil phase containing dissolved solvent; removing said solvent phase from said paraflinic oil phase, and separately recovering said selective solvent from both phases whereby a paraffinic oil having a lower viscosity gravity constant than the original oil is produced and a naphthenic oil of higher viscosity gravity constant than the original oil is likewise produced.

4. In the process of refining petroleum oils by solvent extraction with 5,fi'-dichlorethyl ether, the step of increasing the degree of separation of the naphthenic from the paraflinic hydrocarbons which comprises adding p-methoxy ethanol in the proportion of about one part p-methoxy ethanol to about one to four parts by volume of dichlorethyl ether.

5. In the process of refining petroleum oils by solvent extraction with fl,fl'-dichlorethy1 ether, the step of raising the miscibility temperatures of mixtures of said ether and petroleum oils by the addition of ,e-methoxy ethanol to said mixtures.

JOHN M. RUSS, JR. HARVEY R. FIFE. 

